In a conventional wireless communication system, size of the zone of the wireless base station is decided at a design stage. When a service starts to be provided, the service is provided by the same zone. Factors for determining the zone at the design stage are transmission power, tilt of antennas and the like. The size of the zone can be changed by changing the factors.
FIGS. 1 and 2 show a conventional technique. As shown in FIG. 1, a newly installed wireless base station which is newly mounted searches frequencies and perch channels of surrounding wireless base stations, and determines carrier of the base station (f0) or transmission timing (T0) of perch channel. In this case, the size of the zone is predetermined. In addition, as shown in FIG. 2, the service is provided by keeping the predetermined size of the service area without considering service status of the surrounding wireless base stations.
As mentioned above, as for the conventional wireless base station, transmission power and conditions on the antenna are predetermined at the design stage. When initially setting up the wireless base station, as main operation, surrounding conditions such as transmission power of surrounding base stations are measured. On the basis of the surrounding conditions, the timing broadcasted system information and the carrier are determined as notification information. When the wireless base station detects abnormality of synchronization state with surrounding wireless base stations, or, when the wireless base station changes transmission timing of the wireless base station itself due to effect of perch channel of other base stations, the system needs to be reset and rebooted, or quasi-normal operation is necessary for re-synchronization.
In the above-mentioned conventional technique, in order to change an area for providing a service, it is necessary to change setting of transmission power of the wireless base station after stopping the service, or it is necessary to change the wireless base station itself. In addition, since transmission power and antenna condition should be changed by hand, analysis and the like should be performed before changing the transmission power and the antenna condition in order to forming a zone in consideration of various conditions such as installation state of surrounding wireless base stations. In addition, since the work for changing the transmission power and the antenna condition needs to be done every time when environment such as surrounding base stations, traffic variations or the like is changed, high cost is required for maintenance.
In addition, when wireless base stations are placed successively, traffic condition varies from one base station to another. There are some wireless base stations where traffic is congested. On the other hand, there is a case where there is no traffic congestion in adjacent base stations so that there are available channels. Since there is a case where a user which is in the edge of a service area may want to continue communication even when quality degradation may occur, it is desirable that the service area and another service area of an adjacent wireless base station are overlapped. However, if the service areas are always overlapped regardless of traffic conditions, frequency utilization efficiency is lowered.